The fundamentals overlap — clear structure, direct answers, credible sources — but the engines lean on different pipelines. Perplexity is the most search-like, citing sources inline in real time, so ranking well organically and being freshly indexed matters a lot. Gemini draws heavily on Google's own index and search infrastructure, so classic Google SEO carries real weight. ChatGPT's browsing and retrieval behavior has shifted repeatedly and leans on a mix of Bing-indexed content and its own training data.
In practice, treat strong, well-structured, well-cited SEO as the common denominator, then watch which engine your specific audience actually uses before over-indexing on one.